This application is for renewal of studies on rat cortical neurons grown in tissue culture. Cells are harvested from 15 day rat fetuses, dissociated with trypsin and trituration, plated at low densities and cultures are treated with cytosine arabinoside to kill dividing cells. Synapses regularly form in these cultures and by day 20, cells are large enough to permit intracellular recording. Studies to date have shown that about 30% of the neurons are GABA neurons as judged by GABA uptake autoradiography, and that specific GABA release and GABA synthesizing capacities increase as the cultures mature. We have demonstrated inter-relationships between GABA receptors, picrotoxinin receptors, and benzodiazepine receptors and have compared receptor binding in intact cells and membrane preparations, finding important differences. We plan to correlate chemical, pharmacological, and physiological data hoping to correlate GABA and benzodiazepine receptor regulation with physiological changes. We are searching for effects of culture conditions upon the numbers of GABA neurons, looking for cerebral analogies to the effects so well demonstrated in sympathetic ganglia.